A defect can occur in infrastructures such as a runway of an airport, a road (e.g., an express highway) for cars, a tunnel, and a bridge, due to the use thereof and deterioration with the elapse of time. For example, as the defect, a portion including water accumulated therein or a cavity can be generated inside the infrastructure.
For this reason, by inspecting the infrastructure, it is confirmed whether or not a defect has occurred in the infrastructure. As an inspection method, there is a method of measuring the properties of a road surface and inspecting whether or not the road surface is normal, on the basis of the measured values (see, e.g., PTL 1). For example, the road surface is scanned with a laser beam by using a laser scanner so that a crack ratio, rutting (a standard deviation of irregularities in a cross-sectional direction), and flatness (a standard deviation of irregularities in a longitudinal direction) is obtained, and on the basis of a function of them, a value is calculated. On the basis of the calculated value, it is determined whether or not the road surface is normal.